Development Of Sn-Cu-Cr Active Filler Alloy For Diamond Brazing Application

Synthetic diamond are commonly used as cutting and grinding tools for the machining of hard and brittle materials such as ceramics,stone and tungsten carbide.Active brazing is a promising technique for the fabrication of high-performance diamond abrasive tools,which effectively overcome for the disadvantages of diamond tools prepared by sintering and electroplating methods.However,the high temperature during the brazing process and the associated thermal damage considerably impaired the mechanical properties and joint strength of brazed diamond grits,which resulted in abnormal wear of the abrasive grains during service.Because the unsatisfied service performance,the application of brazing technique for the fabrication of diamond grinding tools is still limited.To reduce the thermal damage of brazed diamond,a new low-temperature Sn-Cu-Cr active filler alloy was developed alloy in this work.Based on the wettability study using Sn-Cr binary alloy,the brazed temperature was determined to ensure the proper wetting on diamond with minimized thermal damage.Moreover,the alloy composition was designed based on brazing temperature as well as the mechanical properties.Comparative study indicated the developed Sn-Cu-Cr alloy can form a reliable bonding of synthetic diamond with enhanced mechanical properties,which can be used as an effective means for the development of high performance brazed diamond tools.The main research work of the paper was summarized as follows:Specifically,the research work contained in this paper can be summarized asfollows:1.The wettability of poly-crystalline CVD diamond by binary Sn-Cr alloy was carried out in a vacuum furnace at both elevating and isothermal temperature.The effects of Cr addition and temperature on the wettability of Sn-Cr on CVD diamond were revealed to identify the reactive wetting mechanism.2.According to the wetting experiment result,the basic requirements for the properties of the active filler alloy was determined,to design the composition Sn-Cu-Cr active filler alloy with proper mechanical properties and solidification characteristics.3.Diamond brazing experiments were carried out using the develop Sn-Cu-Cr filleralloy and commercial Ni-14Cr-10P filler alloy.The surface morphology,interface microstructure,and carbide formation of the diamond brazed using these two types of filler alloys were comparatively analyzed.These information was also used to explain the difference in the thermal damage such as diamond chemical corrosion,graphitization and residual stress of brazed diamond.Eventually,the impact toughness results indicated the mechanical strength of diamond grits brazed using developed Sn-Cu-Cr alloy was significantly higher than that of diamond grits brazed using Ni-14Cr-10P alloy.Based on the analysis of research conducted in this work,the main conclusions can be obtained:1.In-situ observation of contact angle after heating-wetting experiments showed that the addition of 1wt.%Cr into Sn significantly improved the wettability of Sn on CVD diamond.The minimum final contact angle after wetting at 950? was achieved for the Sn-Cr alloy with 4 wt.%Cr content.The addition of 6 wt.%Cr resulted in concentration of solid Cr particles,which would impede fluidity,and hence reduce wettability of the Sn-Cr alloys on the CVD diamond substrate.Elevating and isothermal wetting experiments showed that the Sn-Cr alloy well wetted with CVD diamond at 750?.2.Microstructure characterization indicated that the formation of nano-sized scallop-like Cr₇C₃ grains was responsible for the improved wettability of Sn-Cr alloy on CVD diamond substrate.The wetting temperature affected the growth kinetics of Cr₇C₃,and hence the wettability and the spreading kinetics of Sn-Cr alloys on CVD diamond substrates.3.The best alloy distribution ratio Sn-50Cu-2Cr was selected after comprehensive performance comparison.The alloy structure is mainly composed of Cu3Sn phase,Cu6Sn5 phase and a small amount of?Sn phase and Cr elemental phase,and the liquidus of the alloy is 693.7?,and the micro Vickers-hardness is 231.83 HV_0.3.4.A thin and uniform Cr₇C₃ carbide layer was formed at the diamond interface after the new Sn-50Cu-2Cr filler alloy brazeed the diamond at 750?,and the grains of Cr₇C₃ remain submicron size after the brazing reaction at 950?.5.The impact toughness of diamond abrasive grains brazed with Sn-50Cu-2Cr filler alloy at 750? was significantly higher than that of Ni-14Cr-10P after brazing at 950?.Diamond erosion on the surface of diamond abrasive grains brazed with Ni-free Sn-50Cu-2Cr filler alloy was reduced,and graphite or amorphous carbonization was suppressed,which was the reason for decreasing the thermal damage of diamond abrasive grains.